Process of reducing indigo coloring-matters.



ROBERT WIMMER, OF LU DWIGSl-IAFE TO BADISCHE ANILIN & SODA FABRIK, OF LUDWIGSHAFE NON-l"l lE-R II I N E, GERMANY, ASSIGNOR N-ON-THE- RHINE, GERMANY, A CORPORATION.

PROCESS OF REDUCING INDIGO COLORINGFMATTERS.

Specification of Letters Patent.

Patented Feb. 5, 1907.

Application fil d December 1, 1905. Serial No. 289,854.

T 0 all whom it may concern:

Be it known that I, ROBERT W'IMMER, doctor of philosophy and chemist, a'subjcct of the Kins fen-on-the-Rhine, in the Kingdom of Bavaria, German Empire, have invented new and useful Im rovements in the Process of Re ducing In igo Coloring\iatters, of which the following is a specification.

In the specification of Letters Patent No. 820,900 is described a process for the IGCILC- tion of indigo and similar colcaring-matters by means of iron in strong caustic-alkalisolution.

I have now discovered that indigo and similar coloring-matters (which I will hereinafter refer to as indigo) can be reduced by means of iron without it being necessary to have present such large quantities of caustic alkali, nor, indeed, any caustic alkali, and that iron in the presence of certain alkali salts has the power of reducing indigo, and that therefore in the process described in the aforesaid specification the caustic alkali can be partly or wholly re laced by such alkali salt. The salts which can be used according to this invention are the alkali salts of indigo-white, the alkali carbonates, the alkali phosphates, and the alkali sulfids. The carbonates, phosphates, and sulfids of the alkalies should be used in concentrated solution. The process can be carried out, for instance, by adding indigo and the corresponding quantity of iron to a solution of the disodmm salt of indigo-white, preferably containing at least twenty (20) per cent; of indigo-white. The indi o undergoes reduction and forms the solu le monosodium salt of indigo-white or it separates out in the form of free indigo-white itself, which can by the addition of caustic sopa be converted into the soluble sodium sa t.

The following examples will serve to further illustrate the nature of my invention and the method of carrying it into prhcticalefi'ect;

of Bavaria, residing at Ludwigshabut my invention is not confined to these ex amples. The parts are by weight.

Example 1: Stir together, at a ten'iperature of seventy-five(75) degrees centigrade, one hundred. (I00) parts of a thirty (30) per cent. solution of the disodium salt of indigowhitc, twenty (20) parts of lndigo, and twenty (20) parts of iron powder. After filtration a solution containing forty (40) per cent. of indigo-white is obtained.

Example 2: Grind well together equal parts of indigo powder, sodium-carbonate crystals, and iron powder. On heating the mixture to a temperature of from ninety (90) to one hundred (100) degrees Centigrade reduction to indigo-white takes place. In this example the sodium carbonate can be replaced by three (3). times its weight of sodium phosphate, tNaJIPOQ Example 3: Heat'a solution of four hundred (400) arts of crystallized sodium sulfid in two hun. red (200) parts of water to a temperature of seventy-five (75) degrees centigrade and add one hundred and fifty (150) 1parts of iron powder and then gradually two undred and fifty B. A; S. F. tained.

Now What I claim is (250) parts of indigo pure A solution of indigo-white is ob- 1. The process of reducing indigo coloringmatters by heating them with iron powder in a solution of a hereinbefore-n1entioned alkali salt.

2. The process of reducing indigo coloringmatters by heating them with iron powder in a solution of an alkali salt of indigo-white.

In testimony whereof I have hereunto set my hand in the presence of two subscribing witnesses.

ROBERT IVIMMER.

Witnesses:

J. ALECI. LLOYD, Jos. H. LEUTE. 

